Although efforts are being made to solve some of today's network transparency constraints, the solutions offered are still constrained by the rigid rules of today's North American Numbering Plan (NANP) and the architecture which supports it. That is, each telephone subscriber has a number in the NXX-NXX-XXXX format, where N represents a digit from 2-9 and X represents a digit from 0-9. The first group of three digits indicates the area code or NPA of the subscriber, the second group of three digits indicates a switching exchange or service switching point to which the subscriber is connected, and the last four digits indicates the address of the subscriber within the service switching point. Digits 0 and 1 are of course not available as the first digit (N) to allow operator and long distance services.
With the large increase in telephone devices of one sort or another, an equivalent increase in the demand of telephone numbers has been created. For example, 15 years ago, most telephone numbers were used for fixed Plain Ordinary Telephone Service (POTS) devices. Today, more and more users make use of several devices, such as cellular telephones, pagers, fax machines, modems, etc. This demand has placed a large impact on the pool of numbers available for customers. In some instances, a metropolitan area which used to be served by one area code, now requires several. The problem is of course compounded by the need to assign new telephone numbers to subscribers which move from one region to another. In addition, in the future, numbers must be portable between competing network carriers, namely between the Incumbent Local Exchange Carriers (ILEC) and Competitive Local Exchange Carriers (CLEC).
The same applies to competition between toll carriers, which is especially fierce to capture business customers who have locations which are connected via toll lines.
Generally, the customer is interested in forming a seamless communication network in terms of feature operation, and dialing patterns. It also would like its network to be transparent to calling clients and customers, with calls easily covered, routed and transferred throughout their network as though they were at a single location. Number portability therefore becomes important to them, not only within their private network, but externally as well.
The customer's ability to select an inter-LATA or toll carrier is made possible by a Regulation called equal access (EA). Equal access is an operating company tariff which provides a given subscriber access that is equal in type and quality to every inter-LATA carrier. Each IEC has a dialing arrangement, call-screening technique, routing procedure, billing record, and signalling protocol are required to implement the EA environment.
The EA concept originated in the United States with the modified final judgment (MFJ) of 1982 in which AT&T lost its long-distance monopoly and was also required to divest itself of the Bell operating companies (BOCs). This divestiture action resulted in the formation of seven regional holding companies, each comprised of a number of the original BOCs. Manufacturers have implemented the EA concept according to the regulatory requirements of the 1982 MFJ. The United States EA concept is built on geo-politically defined local access and transport areas (LATAs). A LATA is a fixed non-overlapping geographic area determined at the time of the MFJ ruling. Telecommunication services within a LATA, including local and toll calls within a LATA, are carried by Bell operating companies. Inter-LATA traffic must be carried by an inter-LATA carrier (IC). Today, intra-LATA competition is now allowed in the United States. That is, subscribers have the capability of selecting an alternate intra-LATA carrier for intra-LATA calls as well as an inter-LATA carrier for inter-LATA calls. The BOC must transfer inter-LATA traffic to the IC directly from the end office (EO) or via an intermediate switch called an access tandem (AT). The physical location of an IC within a LATA is referred to as the point of presence (POP).
As indicated above, regulators have requested that once implemented, number portability should be available across competing networks. Unfortunately, network facilitators have been unsuccessfully researching options for delivering a service in which telephone numbers are not tied to equipment locations.
New telephone networks with Advanced Intelligent Network (AIN) concepts have been proposed to support faster development of new services through a network architecture in which network functions and interfaces are standardized providing greater independence between service software and technology.
One service application which makes use of AIN technology for separating dialing from physical routing is Local Number Portability (LNP). The applications are being examined by the Information Industry Liaison Committee (IILC) for extension of LNP concepts. Many options have been discussed and are being investigated. The options to route based on network number ownership fall short, in the sense that they impose various limitations, and are at this time unworkable.
An attempt to provide number portability for a private network is offered in U.S. Pat. No. 4,754,479, which issued to Bicknell et al. In this patent, an arrangement is disclosed for providing station number portability to stations ported from an original switching node to a new switching node which allows the ported station to maintain its original assigned station number. Bicknell et al. is able to achieve this feature by providing a data base, common to each and every switching node located within a portability cluster. Thus, when a calling party attempts to reach a called party, which is now served by a new switching node, the switching node serving the calling party will be able to identify, from the common database, that the called party is now being served by a new switching node and accordingly route the call to that new switching node.
Although Bicknell et al. offer that their service could be expanded to provide a network wide service, they confess that an extensive common database, listing station number and switch associations would be required and that such a large database could only be implemented if space and economic constraints were removed.
The current direction for network evolution is to remove intelligence from the telephone exchange using database query procedures to increase network flexibility. Where initial decisions can be made for launching a query to a database, increased flexibility can be easily obtained, usually with reduced costs. However, the costs increase dramatically when all calls from a specific exchange require this procedure. For example, costs associated with the database query implementation include:
AIN and/or vendor license charges (usually on a per dip basis); PA1 Increase in exchange CPU requirements (factor of 2-5 per call); PA1 Augment of the signalling network; PA1 Database infrastructure required to support queries; and PA1 Database updates to keep all systems current.
Number portability requires the treatment of all calls to a specific number irrespective of the point of origin, making the terminating switch the most logical location to control the call. Initially, this concept seemed to present an inexpensive option for allowing portability, but it was soon realized that as the numbers increase, many additional circuits would be required. At this point, release link trunks can be employed to reduce the connections, but this requires a common protocol and significant interconnection development.
Most solutions carry significant development requirements and it is therefore important to choose the option which can support the requirements over the long term.
Two options are the most widely recognized and popular at present. The first is to use AIN technology to use a query and response procedure for each call to query a database to establish number ownership. The second option is that of Terminating Switch Routing. This proposal consists of the routing of calls using the existing NANP to the expected terminating switch location where, when numbers are owned by another network, calls are then route advanced to that network. In some cases, release link trunks are envisioned to reduce the number of circuits required.
Some problems still exist in implementing these proposed methods, including flash cuts, calls being routed several times between networks and inefficient routing schemes. In addition, the solutions proposed above, are meant to make use of AIN technology. Although AIN is considered a subset of Intelligent Networks (IN), number portability should not be limited to AIN networks only.
A need therefore exists for providing a mechanism to take advantage of these various methods while providing the flexibility to eliminate single option constraints.